Onset of the Messinian Salinity Crisis: Sedimentological, petrographic and geochemical characterization of the pre-salt sediments from a new core (Caltanissetta Basin, Sicily)

The present study aims to reconstruct the environmental changes leading to the Messinian Salinity Crisis during the transition from the Tortonian-Messinian marine conditions to the Messinian evaporitic environments. The core 3AGN2S04, recently drilled in the Caltanissetta Basin (Sicily), was analyzed to reveal the petrographic, mineralogical and geochemical characteristics of the late Tortonian – early Messinian pre-salt sediments. In particular, the facies characterization of the carbonates and organic-rich shales of the Calcare di Base (CdB) member allowed to understand its significance in the paleoenvironmental evolution towards salt deposition and to the reconstruct the brecciation processes inside the CdB. The sedimentological and mineralogical analyzes revealed that core 3AGN2S04 consists of the inner shelf facies of the Tripoli Formation passing to the typical carbonate platform facies of the CdB. The local transition between the upper part of the Tripoli Formation and the CdB member indicates that stressful environmental conditions were constant in the central Mediterranean shelf zones during the late Messinian. The CdB carbonates indicate the occurrence of a carbonate platform characterized by peritidal environments rich in different microbial communities and evaporitic deposits, whereas the embedded organic-rich shales suggest a confined, low energy, anoxic and stratified saline system with high productivity and good preservation of organic matter. A complex set of syndiagenetic brecciation processes, interpreted as in situ brecciation, have profoundly marked the CdB deposits.